Tin lithium compounds of the general formula ##STR1##
are known, wherein R, R' and R" are selected from alkyl, branched alkyl or phenyl. These are used as initiators in anionic polymerization reactions.
The tin functionality has been demonstrated to reduce hysteresis in elastomers and consequently give a tire with reduced rolling resistance such as described in EP 682 035 A2.
Presently, the most cost-effective method for making a tin lithium initiator is to react a triorganotin chloride with lithium metal. Unlike alkyllithiums, however, the formation of the tin lithium species requires the reaction to occur in a polar, aprotic solvent like tetrahydrofuran (THF). ##STR2##
It has been found that a minimum mole ratio of 3:1 THF to tin is required in the synthesis. If the ratio is less than 3:1, some fraction of the reaction (proportional to the deficiency of THF) stops at the ditin stage. NMR analysis discloses that the tributyltin lithium is both monomeric and trisolvated in THF. (See Reich, H. J.; Borst, J. P.; Dykstra, R. R. Organometallics 1994, 13, 1-3). Attempts to remove the THF after the initiator has been synthesized leads to decomposition of the tin lithium back to the ditin compound. Based on the foregoing, THF or a similar Lewis base is required to produce this class of tin lithium initiators using the methods presently known in the art.
THF, as well as other solvents, present several problems. For example, Huang et al have shown that THF leads to increased vinyl content in polymers. Huang, Der-Chi; Tsiang, Raymond Chien-Chao J. Appl. Polym. Sci. 1996, 61(2), 333-342; see also Buzdugan, Emil; Ghioca, Paml Mater. Plast. 1995, 32(2), 127-32. Also, since polymerization reactions are typically carried out in hydrocarbon solvents, THF from the initiator contaminates the hydrocarbon recycle stream in polymer production plants. Therefore, hydrocarbon soluble, tin functionalized anionic initiators free of any Lewis base are desirable.
The present invention relates to a a new class of tin lithium compounds of Formula I EQU RR'R"SnGM' (I)
wherein R, R' and R" may be the same or different and each is independently selected from alkyl, aryl, aralkyl and alkylaryl having from 1 to 15 carbon atoms and wherein each carbon atom may be unsubstituted or substituted, G is a substituted or unsubstituted branched, cyclic or straight chain hydrocarbon having from 1 to 20 carbon atoms, the substitutions comprising one or more aryl groups, and M' is an alkali metal comprising Li, Na or K. PA1 with a compound having the formula (III) EQU XGX' (III) PA1 wherein R, R', R", G and X' are as defined above, PA1 which is reacted with an alkali metal selected from Li, Na or K to form a compound (IV), EQU RR'R"SnGM' (I) PA1 wherein and R, R', R", G and M' are described above. Formula (I) is a tin functionalized alkali metal useful as initiators in anionic polymerization reactions. PA1 wherein R, R' and R" may be the same or different and each are independently selected from alkyl, aryl, aralkyl, and alkylaryl having from 1 to 15 carbon atoms and wherein each carbon atom may be unsubstituted or substituted, G is a substituted or unsubstituted branched, cyclic or straight chain hydrocarbon having from 1 to 20 carbon atoms, the substitutions comprising one or more aryl groups, and M' is an alkali metal comprising Li, Na or K. PA1 wherein R, R' and R" may be the same or different and each is selected from an alkyl, aryl, aralkyl and alkylaryl having from 1 to 15 carbon atoms and wherein each carbon atom may be substituted or unsubstituted, G is a substituted or unsubstituted branched, cyclic or straight chain hydrocarbon having from 1 to 20 carbon atoms, wherein the substitutions may be one or more aryl groups, and M' is an alkali metal comprising Li, Na or K. PA1 wherein R, R' and R" may be the same or different and each is independently selected from alkyl, aryl, aralkyl, alkylaryl, or heteroaryl having from 1 to 15 carbon atoms which may be substituted or unsubstituted. These R groups may be ethers or ketones as well, provided they do not interfere with use of the tin lithium compound in a polymerization reaction. G is a substituted or unsubstituted branched, cyclic or straight chain hydrocarbon having from 1 to 20 carbon atoms, the substitutions comprising one or more aryl groups, and M' is an alkali metal, preferably Li, Na or K. These compounds are substantially free from THF or other solvents that may interfere with their use in polymerization reactions, a common problem found in presently available initiators. PA1 with a compound having the formula (III) EQU XGX' (III) PA1 wherein R, R' and R" are defined as above, i.e. they may be the same or different and are selected from alkyl, aryl, aralkyl, or alkylaryl having from 1 to 15 carbon atoms. Each carbon atom may be unsubstituted or substituted as defined above. M is an alkali metal selected from Li, Na and K. PA1 wherein R, R', R", G and X' are as defined above, which is reacted with an alkali metal selected from Li, Na or K to form a the tin functionalized alkali metal of formula (I), EQU RR'R"SnGM' (I) PA1 wherein and R, R', R", G and M' are as defined above. PA1 wherein R, R', R", G and M' are as defined above. PA1 wherein R, R', R", G and M' are as defined above.
The present invention is also directed to a method for synthesizing tin functionalized alkali metal by reacting an organometallic composition of Formula (I) EQU RR'R"Sn--M (II)
In Formula (I), R, R' and R" may be the same or different and are an alkyl, aryl, aralkyl, or alkylaryl having from 1 to 15 carbon atoms. Each carbon atom may be unsubstituted or substituted. M is an alkali metal selected from Li, Na and K.
In Formula (II), X and X' may be the same or different and each is a halogen. G is a substituted or unsubstituted branched, cyclic or straight chain hydrocarbon having from 1 to 20 carbon atoms, the substitutions comprising one or more aryl groups. The reaction of (I) and (II) forms compound of the Formula IV EQU RR'R"SnGX' (IV)
The present invention is also directed to a method for initiating an anionic polymerization reaction by conducting an anionic polymerization reaction in the presence of an initiator having the formula (I): EQU RR'R"SnGM' (I)
The present invention also provides a method for reducing hysteresis in an elastomer by forming an elastomer by anionic polymerization of at least one monomer with an initiator of the formula (I). EQU RR'R"SnGM' (I)
The present invention will now be described in more detail below.